This invention relates generally to the fabrication of a nano-supported catalyst on a substrate, and more particularly to a method of fabricating a nano-supported catalyst using a thin film deposition approach on a substrate for single walled carbon nanotube growth in a reaction chamber.
Carbon is one of the most important known elements and can be combined with oxygen, hydrogen, nitrogen and the like. Carbon has four known unique crystalline structures including diamond, graphite, fullerene and carbon nanotubes. In particular, carbon nanotubes refer to a helical tubular structure grown with a single wall or multi-wall, and commonly referred to as single-walled nanotubes (SWNTs), or multi-walled nanotubes (MWNTs), respectively. These types of structures are obtained by rolling a sheet formed of a plurality of hexagons. The sheet is formed by combining each carbon atom thereof with three neighboring carbon atoms to form a helical tube. Carbon nanotubes typically have a diameter in the order of a fraction of a nanometer to a few hundred nanometers.
Carbon nanotubes can function as either a conductor, like metal, or a semiconductor, according to the rolled shape and the diameter of the helical tubes. With metallic nanotubes, it has been found that a one-dimensional carbon-based structure can conduct a current at room temperature with essentially no resistance. Further, electrons can be considered as moving freely through the structure, so that metallic nanotubes can be used as ideal interconnects. When semiconductor nanotubes are connected to two metal electrodes, the structure can function as a field effect transistor wherein the nanotubes can be switched from a conducting to an insulating state by applying a voltage to a gate electrode. Therefore, carbon nanotubes are potential building blocks for nanoelectronic devices because of their unique structural, physical, and chemical properties.
Existing methods for the production of nanotubes, include arc-discharge and laser ablation techniques. Unfortunately, these methods typically yield bulk materials with tangled nanotubes. Recently, reported by J. Kong, A. M. Cassell, and H Dai, in Chem. Phys. Lett. 292, 567 (1988) and J. Hafner, M. Bronikowski, B. Azamian, P. Nikoleav, D. Colbert, K. Smith, and R. Smalley, in Chem. Phys Lett. 296, 195 (1998) was the formation of high quality individual single-walled carbon nanotubes (SWNTS) demonstrated via thermal chemical vapor deposition (CVD) approach, using Fe/Mo or Fe nanoparticles as a catalyst. The CVD process has allowed selective growth of individual SWNTs, and simplified the process for making SWNT based devices. However, the choice of catalyst materials that can be used to promote SWNT growth in a CVD process has been limited to only Fe/Mo nanoparticles. Furthermore, the catalytic nanoparticles were usually derived by wet chemical routes, which are time consuming and difficult to use for patterning small features.
Another approach for fabricating nanotubes is to deposit metal films using ion beam sputtering to form catalytic nanoparticles. In an article by L. Delzeit, B. Chen, A. Cassell, R. Stevens, C. Nguyen and M. Meyyappan in Chem. Phys. Lett. 348, 368 (2002), CVD growth of SWNTs at temperatures of 900xc2x0 C. and above was described using Fe or an Fe/Mo bi-layer thin film supported with a thin aluminum under layer. However, the required high growth temperature prevents integration of CNTs growth with other device fabrication processes.
Ni has been used as one of the catalytic materials for formation of SWNTs during laser ablation and arc discharge process as described by A. Thess, R. Lee, P. Nikolaev, H. Dai, P. Petit, J. Robert, C. Xu, Y. H. Lee, S. G. Kim, A. G. Rinzler, D. T. Colbert, G. E. Scuseria, D. Tomanet, J. E. Fischer, and R. E. Smalley in Science, 273, 483 (1996) and by D. S. Bethune, C. H. Kiang, M. S. de Vries, G. Gorman, R. Savory, J. Vazquez, and R. Beyers in Nature, 363, 605 (1993). However, attempts to use a solution based Ni catalyst to grow individual SWNTs by CVD has not been successful. Additionally, although a thin Ni film has been widely used to produce MWNTs, growth of SWNTs using a Ni thin film as the active catalyst film layer has not been achieved.
Accordingly, it is an object of the present invention to provide a new and improved approach for providing a nano-supported catalyst on a substrate for single-walled nanotube growth that allows such nanotubes to be grown at temperatures below 850xc2x0 C. on the substrate using a simplified method that achieves growth of individual single-walled nanotubes, while maintaining the ability to control the density of the SWNTs. The reduced growth temperature also allows one to grow SWNTs on top of pre-patterned metallic electrodes, such as gold, which facilitates electrical field directed SWNTs growth. Furthermore, additional desirable features will become apparent to one skilled in the art from the drawings, foregoing background of the invention and following detailed description of a preferred exemplary embodiment, and appended claims.
To achieve the objects and advantages specified above and others, a method of fabricating a nanotube structure is disclosed which includes providing a substrate, providing a catalyst film comprised of an active film layer supported by a supporting layer, deposited onto the substrate. Single-walled nanotubes are formed from the catalyst using a reaction chamber with a hydrocarbon gas atmosphere at elevated temperatures.